A Multifunctional Catalytic Interlayer for Propelling Solid–Solid Conversion Kinetics of Li₂S₂ to Li₂S in Lithium–Sulfur Batteries

The theoretically high-energy-density lithium–sulfur batteries (LSBs) are seriously limited by the disadvantages including the shuttle effect of soluble lithium polysulfides (LiPSs) and the sluggish sulfur redox kinetics, especially for the most difficult solid–solid conversion of Li₂S₂ to Li₂S. Herein, a multifunctional catalytic interlayer to improve the performance of LSBs is tried to introduce, in which Fe_1–xS/Fe₃C nanoparticles are embedded in the N/S dual-doped carbon network (NSC) composed by nanosheets and nanotubes (the final product is named as FeSC@NSC). The well-designed 3D NSC network endows the interlayer with a satisfactory LiPSs capture-catalytic ability, thus ensuring fast redox reaction kinetics and suppressing LiPSs shuttling. The density functional theory calculations disclose the catalytic mechanisms that FeSC@NSC greatly improves the liquid–solid (LiPSs to Li₂S₂) conversion and unexpectedly the solid–solid (Li₂S₂ to Li₂S) one. As a result, the LSBs based on the FeSC@NSC interlayer can achieve a high specific capacity of 1118 mAh g⁻¹ at a current density of 0.2 C, and a relatively stable capacity of 415 mAh g⁻¹ at a large current density of 2.0 C after 700 cycles as well as superior rate performance.